Update libwebp and resume testing scaled webp

dm/DM.cpp

Index: dm/DM.cpp
diff --git a/dm/DM.cpp b/dm/DM.cpp
index 2a96a9e630f5f00198cf4d696c6cd68c38964dab..e616c187047350bd673a243116ce1aab5a8822e1 100644
--- a/dm/DM.cpp
+++ b/dm/DM.cpp
@@ -302,12 +302,6 @@ static void push_codec_srcs(Path path) {
     }
 
     for (float scale : nativeScales) {
-        if (scale != 1.0f && (path.endsWith(".webp") || path.endsWith(".WEBP"))) {
-            // FIXME: skbug.com/4038 Scaling webp seems to leave some pixels uninitialized/
-            // compute their colors based on uninitialized values.
-            continue;
-        }
-
         for (CodecSrc::Mode mode : nativeModes) {
             for (uint32_t i = 0; i < numColorTypes; i++) {
                 push_codec_src(path, mode, colorTypes[i], scale);